Abstract:

A head for ejecting a liquid from ejection holes, including: a first
flow-passage member in which is formed a first liquid-supply passage; a
second flow-passage member in which is formed a second liquid-supply
passage connected to the first passage and which has outflow ports for
dispensing the liquid from the second passage; a third flow-passage
member in which are formed (a) at least one common liquid passage each
communicating with at least one of the outflow ports and (b) individual
liquid passages; and at least one energy giving member, wherein the first
member, the second member, and the third member are superposed in this
order on each other, and wherein the head further comprises a heater
disposed between one surface of the first member that faces the second
member and facing surface of the second member as one surface thereof
that faces the first member.

Claims:

1. A liquid ejecting head for ejecting a liquid from a plurality of
ejection holes, comprising:a first flow-passage member in which is formed
a first liquid-supply passage to which the liquid is supplied from an
exterior of the liquid ejecting head;a second flow-passage member in
which is formed a second liquid-supply passage connected to the first
liquid-supply passage and which has a plurality of outflow ports for
dispensing the liquid from the second liquid-supply passage;a third
flow-passage member in which are formed (a) at least one common liquid
passage each communicating with at least one of the plurality of outflow
ports of the second flow-passage member and (b) a plurality of individual
liquid passages which are provided so as to respectively correspond to
the plurality of ejection holes, each of which is connected to any one of
the at least one common liquid passage, and which respectively have
pressure chambers formed therein, each of the plurality of individual
liquid passages introducing the liquid to a corresponding one of the
plurality of ejection holes via a corresponding one of the pressure
chambers; andat least one energy giving member configured to give
ejection energy to the liquid in each of the pressure chambers that are
formed respectively in the plurality of individual liquid
passages,wherein the first flow-passage member, the second flow-passage
member, and the third flow-passage member are superposed in this order on
each other, andwherein the liquid ejecting head further comprises a
heater disposed between one surface of the first flow-passage member that
faces the second flow-passage member and facing surface of the second
flow-passage member as one surface thereof that faces the first
flow-passage member.

2. The liquid ejecting head according to claim 1, wherein the second
liquid-supply passage has a first extending passage portion that extends
along the facing surface.

3. The liquid ejecting head according to claim 2,wherein the second
flow-passage member has a laminar structure composed of a plurality of
plates, andwherein the first extending passage portion is provided by an
opening which is formed through a thickness of one of the plurality of
plates that is located intermediate among the plurality of plates in a
direction of lamination of the laminar structure.

4. The liquid ejecting head according to claim 2, wherein the second
liquid-supply passage has a second extending passage portion which
communicates with the first extending passage portion on a downstream
side of the first extending passage portion and which extends along the
facing surface so as to overlap the first extending passage portion as
viewed in a direction perpendicular to the facing surface.

5. The liquid ejecting head according to claim 4,wherein the second
flow-passage member has a laminar structure composed of a plurality of
plates, andwherein the first extending passage portion is provided by an
opening which is formed through a thickness of one of the plurality of
plates that is located intermediate among the plurality of plates in a
direction of lamination of the laminar structure, and the second
extending passage portion is provided by an opening which is formed
through a thickness of another one of the plurality of plates that is
located intermediate among the plurality of plates in the direction of
lamination of the laminar structure and that cooperates with said one of
the plurality of plates to sandwich at least one of the plurality of
plates therebetween.

6. The liquid ejecting head according to claim 2, wherein the second
liquid-supply passage has two first extending passage portions each as
the first extending passage portion.

7. The liquid ejecting head according to claim 6, comprising two heaters
each as the heater, the two heaters being disposed so as to be opposed
respectively to the two first extending passage portions in a direction
perpendicular to the facing surface.

8. The liquid ejecting head according to claim 6, wherein the two first
extending passage portions have the same length as measured in a
direction of extension thereof.

9. The liquid ejecting head according to claim 6,wherein the second
flow-passage member has an elongate shape extended in one direction,
andwherein a direction of extension of each of the two first extending
passage portions coincides with said one direction, and the two first
extending passage portions are arranged in said one direction.

10. The liquid ejecting head according to claim 9, wherein the second
liquid-supply passage is configured such that the liquid flowing in one
of the two first extending passage portions flows in a direction away
from the other of the two first extending passage portions.

11. The liquid ejecting head according to claim 9, wherein the two first
extending passage portions are provided so as to be symmetric with
respect to a plane that includes a center of the second flow-passage
member in said one direction and that is perpendicular to the one
direction.

12. The liquid ejecting head according to claim 9, comprising two heaters
each as the heater,wherein the two heaters are disposed so as to be
opposed respectively to the two first extending passage portions in a
direction perpendicular to the facing surface, and a midpoint of a
distance by which the two heaters are spaced apart from each other
coincides with a center of the second flow-passage member in said one
direction.

13. The liquid ejecting head according to claim 6,wherein the second
liquid-supply passage has two downstream portions each of which is
disposed on a downstream side of a corresponding one of the two first
extending passage portions so as to communicate therewith and which merge
with each other, andwherein the plurality of outflow ports are disposed
more downstream than a merge point at which the two downstream portions
merge with each other.

14. The liquid ejecting head according to claim 13, wherein a resistance
against a flow of the liquid flowing in one of the two first extending
passage portions and one of the two downstream portions connected to said
one of the two first extending passage portions and reaching the merge
point is equal to a resistance against a flow of the liquid flowing in
the other of the two first extending passage portions and the other of
the two downstream portions connected to the other of the two first
extending passage portions and reaching the merge point.

15. The liquid ejecting head according to claim 13, wherein the two
downstream portions function as respective second extending passage
portions which are provided so as to respectively correspond to the two
first extending passage portions and which extend along the facing
surface so as to respectively overlap the two first extending passage
portions as viewed in a direction perpendicular to the facing surface.

16. The liquid ejecting head according to claim 15, wherein each of the
two second extending passage portions has a length as measured in a
direction of extension thereof that is equal to a length of a
corresponding one of the two first extending passage portions as measured
in the direction.

17. The liquid ejecting head according to claim 15,wherein the second
flow-passage member has a laminar structure composed of a plurality of
plates, andwherein each of the two first extending passage portions is
provided by an opening which is formed through a thickness of one of the
plurality of plates that is located intermediate among the plurality of
plates in a direction of lamination of the laminar structure, and each of
the two second extending passage portions is provided by an opening which
is formed through a thickness of another one of the plurality of plates
that is located intermediate among the plurality of plates in the
direction of lamination of the laminar structure and that cooperates with
said one of the plurality of plates to sandwich at least one of the
plurality of plates therebetween.

18. The liquid ejecting head according to claim 1, wherein the heater is
disposed so as to be in contact with the second flow-passage member.

19. The liquid ejecting head according to claim 18, wherein the second
flow-passage member is formed of a material having a higher degree of
heat conductivity than a material of the first flow-passage member.

20. The liquid ejecting head according to claim 18, wherein the heater is
disposed so as not to be in contact with the first flow-passage member.

21. The liquid ejecting head according to claim 1, wherein a clearance is
provided between said one surface of the first flow-passage member that
faces the second flow-passage member and the facing surface of the second
flow-passage member that faces the first flow-passage member.

22. The liquid ejecting head according to claim 21, wherein the hearer is
disposed in the clearance.

Description:

CROSS REFERENCE TO RELATED APPLICATION

[0001]The present application claims priority from Japanese Patent
Application No. 2008-245456, which was filed on Sep. 25, 2008, the
disclosure of which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates in general to a liquid ejecting head
for ejecting a liquid therefrom.

[0004]2. Description of the Related Art

[0005]The viscosity of a liquid such as ink ejected from a liquid ejecting
head varies depending upon the temperature of the liquid. In general, the
viscosity of the liquid is increased under a low temperature condition.
Accordingly, under the low temperature condition, a resistance against a
flow of the liquid at a time when the liquid flows into a pressure
chamber becomes large, so that it is difficult to obtain a satisfactory
ejection effect even if a drive frequency is increased. Further, in order
to obtain, under the low temperature condition, the same ejection
characteristic (including the ejection amount and the ejection speed) as
obtained under an ordinary temperature condition, it is needed to give,
to the liquid in the pressure chamber, ejection energy larger than that
given under the ordinary temperature condition, by increasing a drive
voltage. In this instance, however, it is needed to increase a withstand
voltage of an actuator configured to give the ejection energy to the
liquid in the head and a withstand voltage of a driver IC configured to
drive the actuator. Thus, ejection of the liquid having high viscosity
entails some difficulty.

[0006]In view of the above, the following Patent Document 1 discloses an
ink-jet recording apparatus in which a sub tank, an ink supply pipe
connecting the sub tank and a head chip, and a flow-passage substrate
provided on the head chip are provided with respective heating devices,
for the purpose of lowering the viscosity of the ink under the low
temperature condition.

[0007]Patent Document 1: JP-A-2002-264362

SUMMARY OF THE INVENTION

[0008]The ink-jet recording apparatus disclosed in the above-indicated
Patent Document 1 is provided with the three heating devices, and one of
the three heating devices is disposed outside the head chip, rendering
the structure of the apparatus complicated. Further, even though the
heating device is disposed on the upper surface of the flow-passage
substrate, it is impossible to effectively warm the ink in the head chip,
so that the viscosity of the ink in the head cannot be sufficiently
lowered.

[0009]A need has arisen for a liquid ejecting head capable of effectively
warming a liquid that flows thereinto.

[0010]According to one embodiment herein, a liquid ejecting head for
ejecting a liquid from a plurality of ejection holes may comprise: a
first flow-passage member in which is formed a first liquid-supply
passage to which the liquid is supplied from an exterior of the liquid
ejecting head; a second flow-passage member in which is formed a second
liquid-supply passage connected to the first liquid-supply passage and
which has a plurality of outflow ports for dispensing the liquid from the
second liquid-supply passage; a third flow-passage member in which are
formed (a) at least one common liquid passage each communicating with at
least one of the plurality of outflow ports of the second flow-passage
member and (b) a plurality of individual liquid passages which are
provided so as to respectively correspond to the plurality of ejection
holes, each of which is connected to any one of the at least one common
liquid passage, and which respectively have pressure chambers formed
therein, each of the plurality of individual liquid passages introducing
the liquid to a corresponding one of the plurality of ejection holes via
a corresponding one of the pressure chambers; and at least one energy
giving member configured to give ejection energy to the liquid in each of
the pressure chambers that are formed respectively in the plurality of
individual liquid passages, wherein the first flow-passage member, the
second flow-passage member, and the third flow-passage member are
superposed in this order on each other, and wherein the liquid ejecting
head further comprises a heater disposed between one surface of the first
flow-passage member that faces the second flow-passage member and facing
surface of the second flow-passage member as one surface thereof that
faces the first flow-passage member.

[0011]In the liquid ejecting head described above, the liquid in the head
can be effectively warmed by the heater disposed between the one surface
of the first flow-passage member and the facing surface of the second
flow-passage member which faces that one surface, whereby the viscosity
of the liquid in the head can be sufficiently lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]The above and other objects, features, advantages and technical and
industrial significance of the present invention will be better
understood by reading the following detailed description of a preferred
embodiment of the invention, when considered in connection with the
accompanying drawings, in which:

[0013]FIG. 1 is a vertical cross sectional view showing an internal
structure of an ink-jet printer including an ink-jet head according to
one embodiment of the invention;

[0014]FIG. 2 is an exploded perspective view of the ink-jet head of FIG.
1;

[0015]FIG. 3 is a plan view of a part of a plurality of plates
constituting the ink-jet head of FIG. 1;

[0016]FIG. 4 is a plan view of a part of the plurality of plates
constituting the ink-jet head of FIG. 1;

[0017]FIG. 5 is a plan view of a part of the plurality of plates
constituting the ink-jet head of FIG. 1;

[0018]FIG. 6 is a cross sectional view of a filter support member included
in the ink-jet head;

[0019]FIG. 7 is a schematic cross sectional view of the ink-jet head in
its longitudinal direction;

[0020]FIG. 8 is an enlarged plan view of a part of a flow-passage unit
included in the ink-jet head;

[0021]FIG. 9 is a cross sectional view taken along line IX-IX in FIG. 8;
and

[0022]FIG. 10A is an enlarged cross sectional view of the actuator unit
and FIG. 10B is a plan view of an individual electrode.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0023]Referring to the drawings, there will be explained an embodiment of
the present invention.

[0024]FIG. 1 shows an internal structure of an ink-jet printer including
an ink-jet head as a liquid ejecting head according to one embodiment of
the invention. As shown in FIG. 1, the ink-jet printer generally
indicated at 101 in FIG. 1 has a casing 101a having a rectangular
parallelepiped shape. In the casing 101a, there are disposed: four
ink-jet heads 1 which respectively eject magenta ink, cyan ink, yellow
ink, and black ink; and a sheet conveying mechanism 16. On the inner
surface of the top plate of the casing 101a, a control portion 100 for
controlling operations of the ink-jet heads 1 and the sheet conveying
mechanism 16 is attached. A sheet-supply unit 101b is disposed below the
sheet conveying mechanism 16. The sheet-supply unit 101b is removably
attached to the casing 101a. Below the sheet-supply unit 101b, an ink
tank unit 101c is disposed so as to be detachable from the casing 101a.

[0025]In the ink-jet printer 101, there is formed a sheet delivery path
through which a sheet P is delivered along solid arrows in FIG. 1 from
the sheet-supply unit 101b toward a sheet receiving recessed portion 15.
The sheet-supply unit 101b includes: a sheet tray 11 having a box-like
shape opening upward and accommodating a stack of the sheets P; and a
sheet-supply roller 12 configured to supply an uppermost one of the
sheets P accommodated in the sheet tray 11. The sheet P supplied from the
sheet tray 11 by the sheet-supply roller 12 is delivered to the sheet
conveying mechanism 16 while being guided by sheet guides 13a, 13b and
nipped by rollers of a feed roller pair 14.

[0026]The sheet conveying mechanism 16 includes: two belt rollers 6, 7; an
endless sheet conveyor belt 8 wound around the two rollers 6, 7 so as to
be stretched therebetween; a tension roller 10 which is in contact with
the inner circumferential surface of the sheet conveyor belt 8 at the
lower half portion of the loop of the sheet conveyor belt 8 while being
biased downwardly, thereby applying tension to the sheet conveyor belt 8;
and a platen 18 which is disposed in a region enclosed by the sheet
conveyor belt 8. The platen 18 supports, at a position where the platen
18 is opposed to the ink-jet heads 1, the sheet conveyor belt 8 so as to
prevent the sheet conveyor belt 8 from sagging downward. The belt roller
7 is a drive roller configured to be rotated clockwise in FIG. 1 by a
drive force given to its shaft from a sheet delivery motor 19. The belt
roller 6 is a driven roller configured to be rotated clockwise in FIG. 1
by the movement of the sheet conveyor belt 8 in accordance with rotation
of the belt roller 7. The drive force of the sheet delivery motor 19 is
transmitted to the belt roller 7 through a plurality of gears.

[0027]The outer circumferential surface 8a of the sheet conveyor belt 8 is
silicone-treated so as to have adhesion property. A nip roller 4 is
disposed at a position on the sheet delivery path at which the nip roller
4 faces the belt roller 6 with the sheet conveyor belt 8 interposed
therebetween. The nip roller 4 is configured to press the sheet P
supplied from the sheet-supply unit 101b onto the outer circumferential
surface 8a of the sheet conveyor belt 8. The sheet P pressed onto the
outer circumferential surface 8a of the sheet conveyor belt 8 is conveyed
in a sheet conveyance direction, namely, in a sub scanning direction, (in
the rightward direction in FIG. 1) while being held on the outer
circumferential surface 8s of the sheet conveyor belt 8 owing to its
adhesion property.

[0028]A separation plate 5 is disposed at a position on the sheet delivery
path where the separation plate 5 faces the belt roller 7. The separation
plate 5 separates the sheet P held on the outer circumferential surface
8a of the sheet conveyor belt 8 therefrom. The separated sheet P is
delivered upward while being guided by sheet guides 29a, 29b and nipped
by rollers of each of two feed roller pairs 28. Subsequently, the sheep P
is ejected from an outlet 30 formed at the upper portion of the casing
101a to the sheet receiving recessed portion 15 formed on the upper
surface of the casing 101a.

[0029]The four ink-jet heads 1 respectively eject inks of the mutually
different colors, i.e., magenta, yellow, cyan, and black. Each ink-jet
head 1 has a generally rectangular parallepiped shape having a longer
dimension in a main scanning direction that is perpendicular to the sub
scanning direction. The dimension of each head 1 as measured in the main
scanning direction is larger than the width of the sheet. The four
ink-jet heads 1 are arranged side by side in the sheet conveyance
direction and immovable in the main scanning direction. That is, the ink
jet printer 101 is a printer of a line type.

[0030]The bottom surface of each ink-jet head 1 is made as an ejection
surface 2a in which are formed a plurality of ejection holes 108 (FIG. 9)
through which the ink is ejected. When the sheet P being conveyed passes
right below the four ink-jet heads 1, the inks of the different colors
are ejected from the ejection holes 108 toward the upper surface of the
sheet P, whereby an intended color image is formed on the upper surface,
i.e., on the print surface, of the sheet P.

[0031]The four ink-jet heads 1 are connected respectively to four ink
tanks 17 disposed in the ink tank unit 101c. The inks of the mutually
different four colors are stored in the respective four ink tanks 17. The
inks are supplied from the ink tanks 17 to the respective ink-jet heads 1
via respective tubes.

[0032]FIG. 2 is an exploded perspective view of the ink-jet head 1. As
shown in FIG. 2, the ink-jet head 1 includes: a base plate 31; a
reservoir unit 32 that includes a first flow-passage member and a second
flow-passage member; a head main body 33 that includes a flow-passage
unit 9 as a third flow-passage member; and two sheet-like heaters 34, 35.
FIGS. 3-5 are plan views showing a plurality of components constituting
the head 1, except for the base plate 31 and a COF 51 that will be
explained. As shown in FIGS. 2-5, the reservoir unit 32 is constituted
by: a laminar body 37 including six plates 42-47 and a small-plate group
48; and a filter support member 41 that is fixed to the upper surface of
the laminar body 37. The small-plate group 48 consists of eight inner
small plates 48a and two outer small plates 48b.

[0033]Referring to the cross sectional view of FIG. 6, the filter support
member 41 as the first flow-passage member will be explained. The filter
support member 41 is formed by integral molding of a resin material. In
the filter support member 41, there is formed a first liquid-supply
passage to which the ink is supplied from the ink tank 17. Two
cylindrical projections 70a, 70b project upward from an upper surface 70f
of the filter support member 41. A vertically extending inlet 71 is
formed in the cylindrical projection 70a. To the cylindrical projection
70a, a flexible tube is attached, and the ink in the ink tank 17 as an
ink supply source is introduced into the filter support member 41 from
the inlet 71 via the tube.

[0034]There is formed, in the filter support member 41, an ink flow
passage 73 as the first liquid-supply passage that includes the
vertically extending inlet 71 in which an ink inlet opening is formed and
two vertically extending outlets 72a, 72b in each of which an ink outlet
opening is formed. The ink flow passage 73 includes an intermediate
portion 93 between the inlet 71 and the two outlets 72a, 72b. In the
intermediate portion 93, there is formed an elongate, rectangular opening
74a opening downward.

[0035]To the filter support member 41, there is attached a filter 79 in
which a plurality of minute through-holes are formed for filtering the
ink. The filter 79 divides the intermediate portion 93 into: a first
space 74 which is held in communication with the inlet 71 and which is
defined by the rectangular opening 74a; and a second space 75 which is
held in communication with the outlets 72a, 72b. A region of the second
space 75 which does not face the filter 79, i.e., a non-facing region 76,
horizontally extends at a height level that is slightly higher than a
height level of a region of the second space 75 which faces the filter
79. The two outlets 72a, 72b extend from the non-facing region 76 in the
vertically downward direction so as to open to a lower surface 70e of the
filter support member 41.

[0036]The first space 74 has an elongate, rectangular shape. The opening
74a is sealed by a damper film 78 as a seal member. The damper film 78
has generally the same shape as the opening 74a in plan view. Thus, the
damper film 78 cooperates with the filter support member 41 to define the
ink flow passage 73. A peripheral wall 74b that defines the opening 74a
extends downward to a predetermined height level throughout its
periphery, so that the damper film 78 fixed to the lower end of the
peripheral wall 74b extends horizontally.

[0037]In the second space 75, a downward opening 75a is defined by a
recess. The opening 75a faces a part of the damper film 78 that extends
from a position on a right side of the center of the damper film 78 to
the right-side end of the same 78. The opening 75a has a shape, in plan
view, that tapers in both of a direction of the ink flow and a direction
opposite to the ink flow direction. The filter 79 has a shape
substantially similar to that of the opening 75a and has a size in plan
view somewhat larger than the opening 75a. The filter 79 is fixed in the
first space 74 so as to cover the opening 75a. In other words, the filter
79 is fixed to the filter support member 41 so as to be opposed to the
opening 74a and the damper film 78.

[0038]The ink introduced from the inlet 71 initially flows substantially
horizontally in the first space 74 from the left to the right in FIG. 6,
then reaches the region of the first space facing the filter 79, and
flows upward through the filter 79. Subsequently, the ink flows into the
second space 75 through the filter 79. In this occasion, foreign
substances present in the ink flowed from the first space 74 are caught
by the filter 79, and the ink from which the foreign substances have been
removed by the filter 79 flows in the second space 75. After the ink has
flowed in the non-facing region 76 of the second space 75, the ink flows
downward through the outlets 72a, 72b and is finally discharged into the
plate 42.

[0039]The damper film 78 is a flexible resin film. Between the damper film
78 and the upper surface of the plate 42, there is formed a clearance
that allows deflection of the damper film 78 in accordance with vibration
of the ink. According to the structure described above, the damper film
78 is deflected in the substantially vertical direction in accordance
with the vibration of the ink, whereby the vibration of the ink can be
absorbed and damped.

[0040]An opening is formed in an upper surface 70f of the filter support
member 41 to define the non-facing region 76. The opening is sealed by a
film 76a having flexibility, and the film 76a is deflected in accordance
with the vibration of the ink, whereby the vibration of the ink is
absorbed and damped.

[0041]In the filter support member 41, there is further formed a discharge
passage connecting the first space 74 and an outlet opening of the
cylindrical projection 70b. The discharge passage initially extends below
the non-facing region 76 in the width direction of the filter support
member 41, then extends in the longitudinal direction of the filter
support member 41 after having extended upward to the same height level
as the non-facing region 76, and finally communicates with the
cylindrical projection 70b on the downstream side of a position at which
the discharge passage comes down to a height level lower than the filter
79. A region 77 having the same height level as the non-facing region 76
is defined by sealing an opening formed in the upper surface 70f of the
filter support member 41 with a film 76b. The discharge passage is
utilized for discharging air bubbles staying in a portion of the filter
support member 41 located on the upstream side of the filter 79.

[0042]The laminar body 37 including the plates 42-47 and the small-plate
group 48 constitutes the second flow-passage member. Each of the plates
of the laminar body 37 is formed of a metal material having a higher
degree of heat conductivity than the resin material of the filter support
member 41. In the plates of the laminar body 37, there are formed
through-holes, openings, and a recess which provide the second
liquid-supply passage and eighteen outflow ports described below.

[0043]More specifically, two through-holes 42a, 42b are formed through the
thickness of the plate 42 in the vicinity of the central portion of the
same 42, so as to be opposed to the inlets 72a, 72b, respectively. The
two through-holes 42a, 42b are connected to the ink flow passage 73 as
the first liquid-supply passage. The upper surface of the plate 42 faces
the lower surface 70e of the filter support member 41. In the following
description, the upper surface of the plate 42 is referred to as a
"facing surface".

[0044]Two openings 43a, 43b are formed through the thickness of the plate
43. The opening 43a extends from the vicinity of the central portion of
the plate 43 to one of longitudinal ends of the same 43 while the opening
43a extends from the vicinity of the central portion of the plate 43 to
the other of the longitudinal ends of the same 43. Each opening 43a, 43b
has a tapered section that tapers in a direction toward the central
portion of the plate 43. The openings 43a, 43b are opposed, around ends
of the respective tapered sections, to the through-holes 42a, 42b,
respectively. Two through-holes 44a, 44b are formed through the thickness
of the plate 44 so as to be located at respective longitudinal end
portions of the plate 44. The through-holes 44a, 44b are respectively
opposed to outer ends of the respective openings 43a, 43b.

[0045]An elongate, rectangular opening 45a is formed through the thickness
of the plate 45 so as to extend from one of longitudinal end portions of
the plate 45 to the other of the longitudinal end portions thereof. The
opening 45a is opposed, at its longitudinally opposite ends, to the
respective through-holes 44a, 44b. A circular through-hole 46a is formed
through the thickness of the plate 46 around the central portion of the
same 46. The through-hole 46 has a diameter slightly smaller than the
width of the opening 45a and is opposed to the central portion of the
opening 45a.

[0046]An elongate recess 47a is formed in the plate 47 so as to extend
from one of longitudinal end portions of the plate 47 to the other of the
longitudinal end portions of the same 47. The central portion of the
recess 47a is opposed to the circular opening 46a. The recess 47a is
formed by etching a substantially upper half portion of the plate 47 in
its thickness direction.

[0047]In addition to the recess 47a, eighteen through-holes 47b are formed
through the thickness of the plate 47 so as to be located within the
recess 47a. More specifically, the eighteen through-holes 47b are located
so as to be contiguous to the periphery of the recess 47a and are
arranged, along the longitudinal direction of the plate 47, in two rows
each consisting of nine through-holes 47b. The nine through-holes 47b in
each of the two rows are disposed such that eight through-holes 47b
except for the outermost one of the through-holes 47b form four pairs.
Each pair consists of two through-holes 47a that are located adjacent to
each other. Further, the eighteen through-holes 47b are disposed so as to
have point symmetry with respect to the center of the plate 47.

[0048]In each of eight inner small plates 48a in the small-plate group 48,
there are formed two through-holes 49a which are to be opposed to
corresponding two adjacent through-holes 47b of the plate 47. In each of
two outer small plates 49b between which the eight inner small plates 48a
are disposed, one through-hole 49b is formed so as to be opposed to a
corresponding one of the outermost through-holes 47b in the plate 47.

[0049]In the present embodiment, the second liquid-supply passage is
constituted by the through-holes 42a, 42b formed in the plate 42; the
openings 43a, 43b formed in the plate 43; the through-holes 44a, 44b
formed in the plate 44; the opening 45a formed in the plate 45; the
through-hole 46a formed in the plate 46; and recess 47a formed in the
plate 47, which are in communication with each other. The through-holes
47b in the plate 47 and the through-holes 49a, 49b in the plate 48
constitute a plurality of outflow ports connected to the second
liquid-supply passage. More specifically, each outflow port is
constituted by a combination of the through-hole 47b formed in the plate
47 and the through-hole 48a formed in a corresponding small plate 48a or
the through-hole 49b formed in a corresponding small palate 48b. Each
outflow port is connected to a corresponding manifold 105 in the
flow-passage unit 9 via a corresponding ink supply hole 105b described
below.

[0050]The two heaters 34, 35 are fixed to the facing surface 42c of the
plate 42 so as to be in contact therewith. The length of each heater 34,
as measured in the longitudinal direction of each of the plates 42-47 is
not larger than half the length of each of the plates 42-47 as measured
in the same direction. Each heater 34, 35 has a generally rectangular
shape that extends in the longitudinal direction of the reservoir unit
32, and is disposed on the facing surface 42c such that the longitudinal
direction of each heater 34, 35 coincides with the longitudinal direction
of the reservoir unit 32. A mid point between a line connecting the two
heaters 34, 35 coincides with the center of the laminar body 37, as the
second flow-passage member, that includes the plates 42-47 and the
small-plate group 48. The arrangement reduces a variation in the
temperature in the head 1, thereby reducing a variation in the
temperature of the ink. Accordingly, it is possible to minimize
nonuniformity in the printed image.

[0051]The head main body 33 includes the flow-passage unit 9, ten filters
106, and eight actuator units 21. The filters 106 and the actuator units
21 are fixed to the upper surface of the flow-passage unit 9. Each filter
106 is provided for a corresponding one of the ten small plates 48a, 48b,
and covers one or two ink supply holes 105b which will be explained.

[0052]Each of the eight actuator units 21 includes a plurality of
piezoelectric actuators for giving ejection energy to the ink in
respective pressure chambers 110 (FIG. 9). The COF 51 which is a flat
flexible substrate is bonded to the upper surface of each actuator unit
21. On each COF 51, a driver IC 52 for generating drive signals to be
supplied to the corresponding actuator unit 21 is mounted. In each driver
IC 52, a temperature sensor is disposed. The filter support member 41,
the laminar body 37 as the second flow-passage member including the
plates 42-47 and the small-plate group 48, and the flow-passage unit 9
are stacked on one another in a direction in which the ink flows from the
eighteen outflow ports to the manifolds 105, so as to provide a laminated
structure.

[0053]A plurality of electronic components are disposed on the base plate
31 of the head 1. The two heaters 34, 35 and the COFs 51 are connected to
the electronic components via connectors 31a attached to the base plate
31. The electronic components disposed on the base plate 31 are connected
to the control portion 100 via wires not shown. The operations of the two
heaters 34, 35 are controlled by the control portion 100. As shown in
FIGS. 2 and 3, in the present embodiment, the two heaters 34, 35 have
respective heating portions each as a heat element and respective
temperature sensors 34a, 35a for detecting the temperature of the
corresponding heating portions. Each temperature sensor 34a, 35a is
constituted by a thermister as a thermoelectric element. Only when the
temperature detected by the temperature sensors 34a, 35a is lower than a
prescribed temperature, the heaters 34, 35 are electrified.

[0054]FIG. 7 is a schematic cross sectional view of the head 1 in its
longitudinal direction, in which the base plate 31 is not illustrated. In
FIG. 7, the aspect ratio of each component is largely changed in order
that passages can be easily visible. As shown in FIG. 7, there is formed
a clearance between the facing surface 42c of the plate 42 and the lower
surface of the filter support member 41, facilitating installation of the
heaters 34, 35. The two heaters 34, 35 are fixed to the facing surface
42c of the plate 42 so as to be located within the clearance, without
contacting the lower surface of the filter support member 41. In other
words, the heaters 34, 35 are disposed between two components of the
reservoir unit 32, more specifically, between the facing surface 42c of
the plate 42 and the lower surface of the filter support member 41.
According to the arrangement, a ratio of the heat that escapes to the
exterior of the head 1 with respect to the heat generated by the heaters
34, 35 is made small, whereby the laminar body 37 including the plates
42-47 and the small-plate group 48 can be effectively warmed by the heat
generated by the heaters 34, 35. Consequently, the ink flowing in the
laminar body 37 can be effectively warmed.

[0055]The ink that has flowed from the through-holes 42a, 42b down to the
openings 43a, 43b flows in the openings 43a, 43b in mutually opposite
directions toward the respective longitudinal end or outer end portions
of the plate 43. Each of the openings 43a, 43b is a first extending
passage portion in the second liquid-supply passage extending along the
facing surface 42c of the plate 42. The opening 43a is opposed to the
heater 34 while the opening 43b is opposed to the heater 35, in the
direction of lamination of the plates of the laminar body 37. As
described above, in the present embodiment, the two heaters 34, 35 are
disposed on the facing surface 42c of the plate 42, and the second
liquid-supply passage has the two first extending passage portions that
are opposed to the respective heaters 34, 35. Accordingly, the liquid
(ink) can be effectively warmed by the two heaters 34, 35. Further, the
openings 43a, 43b are passage portions that are the closest to the
heaters 34, 35 in the above-indicated lamination direction, so that the
ink flowing in the openings 43a, 43b can be more effectively warmed owing
to the plates 42, 43, 44 that have absorbed the heat of the haters 34,
35.

[0056]The ink that has flowed from the openings 43a, 43b down to the
opening 45a of the plate 45 via the through-holes 44a, 44b of the plate
flows in the opening 45a in mutually opposite directions toward the
center of the plate 45. The opening 45a includes two second extending
passage portions one of which corresponds to a right half portion of the
opening 45a and the other of which corresponds to a left half portion of
the same 45b, as seen in FIG. 7. The two second extending passage
portions extend along the facing surface 42c of the plate 42 and
respectively overlap the openings 43a, 43b each as the first extending
passage portion, as viewed in the lamination direction of the plates of
the laminar body 37. The two second extending passage portions merge with
each other at the upstream end of the through-hole 46a of the plate 46.
(The upstream end of the through-hole 46a will be hereinafter referred to
as a "merge point" where appropriate.) The ink flowing in the two second
extending passage portions can be effectively warmed owing to the plates
44, 45, 46 that have absorbed the heat of the heaters 34, 35.

[0057]In the present embodiment, a resistance against a flow of the ink
that flows from the inlet, i.e., the upstream end, of the through-hole
43a to the merge point (i.e., the upstream end of the through-hole 46a)
is equal to a resistance of a flow of the ink that flows from the inlet,
i.e., the upstream end, of the through-hole 43b to the merge point (i.e.,
the upstream end of the through-hole 46a. Therefore, there is not caused
a difference between the amount of ink that flows in the through-hole 43a
and the amount of ink that flows in the through-hole 43b, whereby it is
less likely to be caused a difference in the temperature of the ink in
the opening 43a and the temperature of the ink in the opening 43b, which
inks are to mix with each other at the merge point. As a result, the
temperature of the ink after having mixed tends to be uniform, thereby
reducing a variation in the temperature of the ink that flows into the
respective eighteen outflow ports. Accordingly, it is possible to
minimize nonuniformity in the printed image.

[0058]In the present embodiment, the opening 45a has a length about twice
as large as each of the openings 43a, 43b. In other words, a length of
each of the two second extending passage portions from its inlet
(corresponding to one longitudinal end of the opening 45a) to its outlet
(corresponding to the central portion of the opening 45a) is equal to a
length of the opening 43a or 43b as the first extending passage portion
from its inlet (corresponding to the inner end of the opening 43a or 43b)
to its outlet (corresponding to the outer end of the opening 43a or 43b).
Since the second extending passage portions are long, the temperature of
the ink can be easily raised by the heaters 34, 35.

[0059]The ink flow as a result of merging of the ink flows in the
respective two second extending passage portions at the merge point
(i.e., the upstream end of the through-hole 46a) drops into the recess
47a of the plate 47 from the downstream end of the through-hole 46a. Then
the ink flows in the recess 47a and subsequently flows into the
flow-passage unit 9 via the eighteen outflow ports provided by the
through-holes 47b and the through-holes 49a, 49b. In the present
embodiment, in the laminar body 37, two downstream portions which are
located on the downstream side of the corresponding openings 43a, 43b
merge with each other, and the eighteen outflow ports are connected to
the second liquid-supply passage on the downstream side of the merge
point. Accordingly, it is possible to reduce a variation in the
temperature of the ink that flows into the eighteen outflow ports.

[0060]In the present embodiment, the laminar body 37 is formed of the
material having heat conductivity higher than that of the material of the
filter support member 41, and the two heaters 34, 35 are fixed so as to
be in contact with the facing surface 42c of the plate 42. Accordingly,
the heat generated by the two heaters 34, 35 can be efficiently
transmitted to the ink. Moreover, the temperature sensors 34a, 35a are
integrally disposed on the respective heaters 34, 35, so that it is
possible to directly detect, without delay, changes in the temperature of
the plates 42 and so on that are caused by the heat generated by the
heaters 34, 35.

[0061]Referring next to FIGS. 8, 9, 10A, and 10B, the head main body 33
will be explained in detail. FIG. 8 is a plan view showing a part of two
adjacent actuator units 21. FIG. 9 is a partial cross sectional view of
the flow-passage unit 9 along line IX-IX in FIG. 8. FIG. 10A is an
enlarged cross sectional view of an area enclosed by the dashed line in
FIG. 9 and FIG. 10B is a plan view of an individual electrode. In FIG. 8,
apertures 112 that should be indicated by a broken line are indicated by
a solid line for easier understanding.

[0062]As shown in FIG. 8, a plurality of pressure chambers 110 each having
a generally rhombic shape are regularly disposed in a matrix on the upper
surface of the flow-passage unit 9. Each actuator unit 21 includes a
plurality of individual electrodes 135 (FIG. 10A) disposed so as to be
respectively opposed to the plurality of pressure chambers 110 formed in
the flow-passage unit 9. The actuator unit 21 has a function of
selectively giving ejection energy to the ink in the pressure chambers
110.

[0063]The ink supply holes 105b (FIG. 5) are open to the upper surface of
the flow-passage unit 9 so as to respectively correspond to the eighteen
outflow ports of the reservoir unit 32. The ink supply holes 105b are
covered with corresponding filters 106 each having a smaller mesh size
than the filter 79. In the flow-passage unit 9, there are formed: a
plurality of manifolds 105 each extending from a corresponding one of the
ink supply holes 105b; and a plurality of sub manifolds 105a, each as a
common liquid passage, which are branched from corresponding manifolds
105. On the lower surface of the flow-passage unit 9, the ejection
surfaces 2a are arranged in each of which a plurality of ejection holes
108, each as a nozzle opening, are regularly arranged in matrix.

[0064]As shown in FIG. 9, the flow-passage unit 9 is constituted by nine
metal plates including a cavity plate 122, a base plate 123, an aperture
plate 124, a supply plate 125, three manifold plates 126, 127, 128, a
cover plate 129, and a nozzle plate 130, which are arranged in this order
from the top of the flow-passage unit 9. Each of the nine plates 122-130
has a rectangular shape in plan view which is long in the main scanning
direction.

[0065]The nine plates 122-130 are positioned with and stacked on each
other, whereby a plurality of individual ink passages 132 as a plurality
of individual liquid passages are defined in the flow-passage unit 9 each
of which extends from an outlet of a corresponding one of the sub
manifolds 105a to a corresponding one of the ejection holes 108 via a
corresponding one of the pressure chambers 110. The ink which has
supplied from the reservoir unit 32 to the flow-passage unit 9 via the
ink supply holes 105b flows into the sub manifolds 105a from the
manifolds 105. The ink in the sub manifolds 105a flows into the
individual ink passages 132 and reaches nozzle ejection holes 108 via the
apertures 112 each functioning as an orifice and the pressure chambers
110.

[0066]The actuator unit 21 will be explained. As shown in FIG. 5, the
eight actuator units 21 each having a trapezoidal shape in plan view are
arranged in a zigzag fashion in the longitudinal direction of the
flow-passage unit 9 so as to avoid the ink supply holes 105b. Parallel
facing sides (short and long sides) of each actuator unit 21 are parallel
to the longitudinal direction of the flow-passage unit 9, and oblique
sides of neighboring two actuator units 21 partially overlap as viewed in
the longitudinal direction of the flow-passage unit 9, namely, in the
main scanning direction, as shown in FIG. 8.

[0067]As shown in FIG. 10A, each actuator unit 21 includes three
piezoelectric layers 141-143 formed of a ceramic material of lead
zirconate titanate (PZT) having ferroelectricity. The individual
electrodes 135 are formed on respective regions of the uppermost
piezoelectric layer 141 that correspond to the pressure chambers 110. A
common electrode 134 is provided on an interface between the uppermost
piezoelectric layer 141 and the piezoelectric layer 142 located under the
layer 141. As shown in FIG. 10B, each individual electrode 135 has a
generally rhombic shape in plan view similar to the pressure chamber 110.
One acute end portion of the individual electrode 135 extends beyond the
pressure chamber 110, and a circular land 136 is formed at the acute end
portion for electrical connection with the individual electrode 135. In
addition to the lands 136 for the individual electrodes 135, a land for
the common electrode 134 is formed on the upper surface of the
piezoelectric layer 141. The land for the common electrode 134 is
connected to the common electrode 134 via the conductive material in
through-holes.

[0068]The common electrode 134 is kept at a ground potential as a basic
potential given by the COF 51. The individual electrodes 135 are
electrically connected to terminals of the driver IC 52 via the
respective lands 136 and respective internal wires of the COF 51. A drive
signal for driving the actuator unit 21 is supplied from the driver IC 52
to the individual electrodes 135 independently of each other.
Accordingly, respective portions in the actuator unit 21 sandwiched by
and between the individual electrodes 135 and the pressure chambers 110
function as individual actuators which are independent of each other.
That is, a plurality of actuators, each as an energy giving member, are
provided in the actuator unit 21 in the same number as the pressure
chambers 110.

[0069]There will be next explained a method of driving each actuator unit
21 to permit ink droplets to be ejected from the nozzles. The
piezoelectric layer 141 is polarized in its thickness direction. When an
electric field is applied to the piezoelectric layer 141 in the
polarization direction with one individual electrode 135 kept at a
potential different from that of the common electrode 134, a portion of
the piezoelectric layer 141 to which the electric field is applied
functions as an active portion that undergoes strain owing to a
piezoelectric effect. The active portion expands in a direction of
thickness of the layer 141 and contracts in a direction parallel to the
plane of the layer 141 (i.e., in the plane direction) when the electric
field and the polarization are in the same direction. In this instance,
the amount of deformation of the active portion upon expansion and
contraction is larger in the plane direction than in the thickness
direction. In the actuator unit 21, the uppermost one 141 of the three
piezoelectric layers that is the most distant from the pressure chambers
110 is an active layer including the active portions while the lower two
piezoelectric layers 142, 143 nearer to the pressure chambers 110 are
non-active layers. As shown in FIG. 10A, the piezoelectric layer 143 is
fixed to the upper surface of the cavity plate 122 that defines the
pressure chambers 110. Accordingly, when there is generated a difference
in strain in the plane direction between the portion of the piezoelectric
layer 141 to which the electric field is applied and the piezoelectric
layers 142, 143 located under the layer 141, the entirety of the
piezoelectric layers 141-143 deforms into a convex shape that protrudes
toward the pressure chamber 110 (unimorph deformation). Accordingly, the
pressure (ejection energy) is given to the ink in the pressure chamber
110, so that there is generated a pressure wave in the pressure chamber
110. The generated pressure chamber propagates from the pressure chamber
110 to the ejection hole 108 of the corresponding nozzle, whereby the ink
droplets are ejected from the ejection hole 108.

[0070]In the illustrated embodiment, the ink that flows in the laminar
body 37 can be effectively warmed by the heaters 34, 35 disposed between
the facing surface 42c of the plate 42 and the lower surface of the
filter support member 41. Accordingly, the viscosity of the ink in each
head 1 can be sufficiently lowered. Hence, even under the low temperature
condition, the resistance against the flow of the ink at a time when the
ink flows into the pressure chamber 110 does not become high, so that
increasing the drive frequency becomes effective for obtaining a
satisfactory ejection effect.

Further, the same ejection characteristic as obtained under the ordinary
temperature condition can be obtained under the low temperature condition
without increasing the drive voltage, so that it is not required to
increase the withstand voltage of the actuator units 21 and the withstand
voltage of the driver ICs 52 configured to drive the actuator units 21.

[0071]It is to be understood that the invention is not limited to the
details of the illustrated embodiment, but may be embodied with various
changes and modifications, which may occur to those skilled in the art,
without departing from the spirit and scope of the invention defined in
the attached claims. For instance, the heaters 34, 35 may be disposed on
the lower surface of the filter support member 41. Only one heater or
more than three heaters may be used. Only one through-hole may be formed
in the plate 42. Only one opening may be formed in the plate 43. Two
openings may be formed in the plate 45. Only one common liquid passage
may be formed in the flow-passage unit 9. The passage structure in the
head 1 is not limited to that in the illustrated embodiment, but may be
otherwise modified. The energy giving member is not limited to the one
utilizing the piezoelectric body, but the one of a thermal type may be
utilized.

[0072]It is to be understood that the principle of the invention may be
applicable not only to the head for a line printer as in the illustrated
embodiment, but also to a head for a serial printer, and further to a
head for ejecting a liquid other than the ink.